Light metering is a process of measuring a brightness of an object to be photographed, which is a basis of automatic exposure of a camera so as to capture images in pictures. Accurate light metering and correct light metering manner selection are often the starting point of photography creation.
For example, generally the light metering manner of a light metering system of a digital camera is Through The Lens (TTL), which meters the intensity of light reflected by an object to be photographed through the lens. A light metering sensor is placed in a photography light path, and light is reflected from a retroreflector onto a light metering element for light metering. Light intensity data is transmitted to a processor of the camera, and an exposure combination, such as a combination of a shooting aperture and a shutter speed, is then determined. According to different areas, sizes and calculation weights metered in a viewfinder coverage by the light metering sensor, light metering manners may be classified into: average metering, center-weighted metering, spot metering, matrix metering and other modes.
For example, in spot metering, a light metering range is a region at the center of a viewfinder image that occupies approximately 1-3% of the entire image area. Spot metering is typically not influenced by the brightness of other sceneries outside a light metering area. Therefore, spot metering may be used to meter the brightness of respective regions of an object to be photographed or a background area.
Along with the wide application of touch screens, using a camera or a smartphone provided with a touch screen, a user may select a position for spot focusing by clicking a spot on a preview interface, thereby improving the utility of spot metering.
In conventional technologies of spot metering, firstly a light metering spot is determined, which may be a center spot in a preview interface, or a spot in a preview interface selected by a user through a touch screen. Then a rectangle or a circle is generated by taking the light metering spot as a center, which may deviate toward a center region when reaching a boundary of the screen. During light metering, the rectangle or the circle may be used as the light metering range.